JT-60U MONTHLY SUMMARY

November 1997

OPERATION AND CONFINEMENT PHYSICS

After the divertor modification, the systematic experiments for the halo
current analyses have been conducted at the plasma current (Ip) <2MA
as an ITER physics R&D. The summary of the experiments shows that the
ratio of the maximum local halo current to the plasma current (Ihmax/Ip0)
is less than 0.52, which satisfies the design condition of ITER (Ihmax/Ip0<0.58).

A careful analysis of transport coefficients was carried out for the reversed
shear discharge with the ELMing H-mode edge where the internal transport
barrier (ITB) located just inside the minimum safety factor position was
sustained for 1.5-2 sec. The analysis shows that the thermal diffusivities
both for electron and ion drop quickly across ITB in the quasi steady state.

These results were presented both in the 38th Annual Meeting of American
Physics Society Division of Plasma Physics (APS-DPP) and in the 14th anniversary
meeting of Japan Society of Plasma Science and Nuclear Fusion Research (Osaka).

CURRENT DRIVE AND HIGH ENERGY PARTICLE PHYSICS

Regarding current drive study, the profile of beam driven current by NNB
injection (360 keV, 2-4 MW) was well identified with MSE measurements and
EFIT code introduced from DIII-D. The identified NNB-driven current profile
agrees reasonably with the predictions by ACCOME code. Controllability of
plasma current was confirmed by the measured profiles of beam driven current
with both NNB and PNB (Positive ion-based NB: 80 keV, 1.2 MW).

The TAE-like mode activities were observed with the NNB injection (350 keV,
~3 MW) for the first time. The mode frequency was 40-130 kHz and the toroidal
mode number was n=1-3. These TAE-like modes show bursting activities similar
to the TAE modes observed using tangential neutral beams in TFTR and DIII-D.
The volume-averaged beta of NNB-injected ions was ~0.2 %, which was roughly
a half of the threshold value of the TAE mode excitation in TFTR and DIII-D.

DIVERTOR AND BOUNDARY PHYSICS

The following results were presented in the 14th anniversary meeting of
Japan Society of Plasma Science and Nuclear Fusion Research and in the APS-DPP
meeting in Pittsburgh.
1) Large gas puff is possible in ELMy H-mode with keeping electron density
almost constant, which will be advantageous to produce SOL flow.
2) Helium exhaust from the private flux region like ITER was successfully
demonstrated in W-shaped divertor.
3) Onset density of X-point MARFE after the divertor modification was decreased
to about 60% of Greenwald density limit , while the onset density of X-point
MARFE in the open divertor was about 70% of Greenwald density limit.
4) High power and long pulse discharges with input energy up to 203 MJ became
possible in the W-shaped divertor.
5) Divertor density in ohmic plus short pulse ICRF heating could be measured
with mm-wave interferometer. Sharp drop in divertor electron density was
observed at the timing of L-H transition.
6) Hydrocarbon generation estimated by CD band intensity decreased and carbon
concentration in the main plasma decreased when divertor pump was active,
suggesting that SOL flow might be produced by gas and pump.